TY - JOUR
T1 - Linear free energy of activation relationship for barrierless association reactions
AU - De Sainte Claire, Pascal
AU - Peslherbe, Gilles H.
AU - Wang, Haobin
AU - Hase, William L.
PY - 1997/5/28
Y1 - 1997/5/28
N2 - An analysis of variational transition state theory rate constants, for the association reactions Cl- + CH3-Cl, Cl- + CH3Br, H+ CH3, H+ diamond {111}, CH3 + CH3, and Al + Al2 shows that the free energy of activation ΔG varies nearly linearly with temperature, over a broad temperature range, for each reaction. This suggests that association rate constants can be parametrized by the free energy of activation at 300 K, ΔG300/(+), and the change in ΔG(+) with temperature, ΔΔG(+)/ΔT. The near linear dependence of ΔG(+) with temperature is supported by a semiempirical model for association kinetics. The rate constants for Cl- + CH3Cl, Cl- + CH3Br, and CH3 + CH3 decrease with increase in temperature, while those for H + CH3, H + diamond{111}, and Al + Al2 slightly increase. For the six association reactions considered here, the linear free energy relationship gives semiquantitative rate constants over a rather broad temperature range of 200-2000 K. To calculate accurate rate constants over a broader temperature range, particularly at low temperatures, nonlinear terms must be included in the free energy expansion.
AB - An analysis of variational transition state theory rate constants, for the association reactions Cl- + CH3-Cl, Cl- + CH3Br, H+ CH3, H+ diamond {111}, CH3 + CH3, and Al + Al2 shows that the free energy of activation ΔG varies nearly linearly with temperature, over a broad temperature range, for each reaction. This suggests that association rate constants can be parametrized by the free energy of activation at 300 K, ΔG300/(+), and the change in ΔG(+) with temperature, ΔΔG(+)/ΔT. The near linear dependence of ΔG(+) with temperature is supported by a semiempirical model for association kinetics. The rate constants for Cl- + CH3Cl, Cl- + CH3Br, and CH3 + CH3 decrease with increase in temperature, while those for H + CH3, H + diamond{111}, and Al + Al2 slightly increase. For the six association reactions considered here, the linear free energy relationship gives semiquantitative rate constants over a rather broad temperature range of 200-2000 K. To calculate accurate rate constants over a broader temperature range, particularly at low temperatures, nonlinear terms must be included in the free energy expansion.
UR - http://www.scopus.com/inward/record.url?scp=0030990527&partnerID=8YFLogxK
U2 - 10.1021/ja961239b
DO - 10.1021/ja961239b
M3 - Article
AN - SCOPUS:0030990527
VL - 119
SP - 5007
EP - 5012
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 21
ER -